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The Chord Organ was first introduced by the Hammond Organ Company in 1950. It was invented primarily by John M. Hanert, who was Hammond's primary musical engineer at the time. He had previously developed the Novachord and Solovox, two instruments which used vacuum-tube circuitry rather than tone or phonic wheels to generate the tones as in a Hammond Organ.

The Chord Organ, as the name implies, used a left-hand panel with buttons to play harmony; however, instead of a Stradella-type chord and bass arrangement, a completely new design was implemeted. 96 separate chord buttons provided Major, Minor, 7th, Diminished, Augmented, Major 6th, Minor 7th and Ninth chords for all twelve musical keys. Two bass pedals, played by the left foot, sounded the "root" and "fifth" of each chord, and rhythm was added by means of a bar struck by either the palm or the thumb of the left hand.

The Chord Organ incorporated elements of both the Novachord and the Solovox in that the right-hand 37-note keyboard could play both chords and single notes. An "Organ" section provided String and Flute sounds which were polyphonic, while a "Solo" division permitted the organist to play single-note melodies superimposed over the polyphonic "Organ" division. The Solo division operated essentially identically to the Solovox - one group of controls determined the register or pitch in which the Solo division would sound while another group of controls allowed the player to filter the sound in various ways ("timbre" controls).

There were five different versions of the basic Chord Organ, which was called the "S" series. The original model "S" used octal tubes and one 12" speaker, the "S-1" used miniature tubes and one 12" speaker. For the "S-4," two 10" speakers were substituted for the single 12" speaker and the wood cabinet was re-designed. The "S-6," the most popular model, added the ability to add Percussion to the Solo division, thereby allowing the instrument to imitate instruments such as Banjo, Hawaiian Guitar, etc. The "S-100," the last revision of the "S" series, added built-in Stereo Reverberation, substituted an Expression Pedal for the expression lever used on previous models and a re-styled cabinet design as well as a separate ON/OFF Power Switch (on previous models, power was turned on by swinging the expression lever down similar to the Solovox).

An additional Chord Organ was manufactured for a brief time in the mid 60's (the "2000 series), which had a simplified chord panel (Major, Minor, 7th and Diminished chords only) and traditional organ-type voices for the right-hand keyboard. This model also used solid-state circuitry.

^English Wikipedia article Accordion#History (as of 17 April 2017 (UTC)): "The accordion is one of several European inventions of the early 19th century that used free reeds driven by a bellows. An instrument called accordion was first patented in 1829 by Cyrill Demian, of Armenian origin, in Vienna. / Demian's instrument bore little resemblance to modern instruments. It only had a left hand buttonboard, with the right hand simply operating the bellows. One key feature for which Demian sought the patent was the sounding of an entire chord by depressing one key. His instrument also could sound two different chords with the same key; one for each bellows direction (a bisonoric action)."

^WurlitzerModel 4100 BP (1959–1963) has a chord unit on the lower left. (For details, see image)

^"Farfisa Model VIP-205R". Combo Organ Heaven. It has a rather unusual (for a combo organ) "Chords" feature. When activated, pressing any key in the first two octaves plays a chord (1st octave: Major, 2nd octave: Minor). The chord continues to sound after key release until you press another "chord" key. (For details, see image)

^"Estey Organs: 1959-1968". MagnatoneAmps.com.Note: according to the model number table at the tail, "electric solid state chord organ" (i.e.electric chord organ) was existence during 1961–1966, and reed chord organ was released in 1966.